Container closure



Sept. 19, 1961 J. B. DONALDSON CONTAINER CLOSURE Filed Sept. 50, 1955 United States Patent Q 3,000,304 CONTAINER (ILOSURE James B. Donaldson, Cooksville, Ontario, Canada, assignor to T. W. Hand Fireworks Co. Limited, Cooksville, Ontario, Canada, a corporation of Canada Filed Sept. 30, 1955, Ser. No. 537,839

1 Claim. (Cl. 102-39) This invention relates to an improved method of closing containers and to a container having an improved closure.

One of the problems which have inhibited the full development of the use of thermoplastic materials for containers has been that of providing a satisfactory closure which can readily and conveniently be applied after the container has been filled. The heat sealing of a thermoplastic closure is not satisfactory for all purposes since the material must be softened to a considerable degree to obtain a good seal. This is time consuming, apt to result in deformation of the container and is particularly objectionable when the contents of the container are of an explosive or inflammable nature. Furthermore, it is often necessary to apply pressure during the heat sealing. This involves additional equipment and in addition pressure cannot easily be applied without damage to the container or closure where it is desired to apply a flat disc type closure. The use of adhesives to attach the closure is unsatisfactory due to the manipulative steps involved, the necessity for a substantial gluing surface and the difiiculty of avoiding defects under extremes of temperature. Furthermore, in the case of material such as polyethylene, no inexpensive effective adhesive is known.

The object of this invention is to provide a closure which can readily be applied and which will provide an efiective seal under a wide range of temperature conditions.

This invention involves the use of a sharp edged disc which may, for example, be of thin sheet metal and which is made slightly larger that the open end of the container. This disc is inserted in place in the open end of the container causing the side walls of the container to be stretched or bulged outwardly. Heat is then applied to soften the side walls causing the side walls to return to their former position and at the same time causing the edge of the disc to become embedded in the side wall. Preferably the elasticity of the side walls of the container is relied upon to restore the side walls but if necessary slight pressure can be used. It has been found that an exceedingly effective closure is provided.

In the drawings which illustrate the preferred embodiments of this invention:

FIGURE 1 is a sectional elevation view of a cartridge case showing the first step in inserting the closure.

FIGURE 2 is a view similar to FIGURE 1 showing the completed closure.

FIGURE 3 is a plan sectional view on the line IIIIII of FIGURE 2.

FIGURE 4 is a diagrammatic view illustrating a suitable apparatus for use in applying the closure.

FIGURE 5 is a sectional elevation view showing an alternative embodiment of the invention in which a bottom closure is provided for a different kind of container.

liferring now to FIGURES 1 to 3 of the drawings, the container to which the closure is being applied is a cartridge case having side Walls 11 and a base 12 integrally molded from elastic thermoplastic material. The preferred material for the side walls and base of the cartridge case is polyethylene but other elastic thermo plastic materials having adequate rigidity can be used. A polyethylene formulation having a Shore A hardness of 55 and a molecular weight of 22,000 is suitable. The polyethylene is compounded with 25% to 45% of inert fillers such as calcium carbonate, about 2% of lubricating agents such as mineral oil or synthetic wax and about 1% to 2% of colouring pigments. The side walls 11 define an opening 13. The cartridge case is fitted with a detonating cap 14 and is filled with an appropriate charge 15 which is retained in position by a disc 16 which may be of cardboard and a supporting paper plug 17. The closure for opening 13 is provided by a sharp edged disc 18. Disc 18 has a flat central portion 19 and a series of annular corrugations 20 terminating in an outwardly flared sharp edge 21. Preferably, disc 19 is made from thin sheet metal such as 0.01" thick tinplate. In this case the edge will be sufliciently sharp without tapering. The annularly corrugated disc structure has the dual advantages of strengthening the disc against bending and of providing a structure which will absorb pressure without displacement of the disc if the disc is subjected to pressures such as an accidental external force on those due to the expansion of the contents, the central portion 19 will move inwardly or outwardly to absorb the pressure due to a partial unfolding of the corrugations. This partial unfolding tends to enlarge the area of the disc to increase the firmness with which the closure is retained. The outwardly flared edge 21 gives additional resistance to internal expansive forces, as when the closure is in place expansion of the contents causes the edge 21 to dig more deeply into the material of the side wall.

FIGURE 1 shows the first stage in which disc 18 is inserted into place in opening 13. Disc 18 is of larger diameter than the interior diameter of side wall 11 but is less than the exterior diameter of side wall 11, accordingly side wall 11 will bulge outwardly as shown at 22 to accommodate the disc. Side wall 11 is then heated to soften the thermoplastic material. It is best that the heating be localized to the portion 22 of the side wall against which the edge of disc 18 bears. This is particularly important where, as in the case of the cartridge, the contents are explosive or inflammable. When portion 22 of the side wall has been softened the resilience of the elastic thermoplastic material Will cause the side wall to straighten to its former position as illustrated in FIGURE 2. This embeds the edge 21 of the disc in the side wall. A particular advantage is that it is SUffiClCl'lt to heat the side wall to a temperature at which the edge of the disc cuts into the material of the side wall. The temperature of the side wall need not be as high as that which Would be required for conventional heat sealing. It has been found that not only does the foregoing procedure cause the disc 18 to become embedded in the side wall but also gives rise to a degree of adhesion between the side wall and the disc. This adhesion increases the effectiveness of the seal between the closure and the side wall. The use of a metal disc with induction heating has the advantage that the metal is heated very rapidly, with the consequence that the side wall of the container is heated by the metal at the point at which it is desired that the metal incise the side wall.

FIGURE 4 illustrates diagrammatically a suitable apparatus for heating portion 22 of the side wall comprising radio frequency generator 23 energizing an induction coil 24. An example of a suitable generator for sealing cartridge cases is a l kva. generator. The induction coil is spaced about A from the side wall of the cartridge 10 and is energized for about /20 of a second. It will be appreciated that the short time needed to complete the closure enables a high rate of production to be obtained.

FIGURE 5 shows a different type of container in which a container 25 is shaped to provide a nozzle 26 and a side wall 27, is filled with contents 28 such as toothpaste, liquid mustard or oil and is filled with a disc 29 to provide a bottom closure of the same structure and in a similar manner as disc 18.

I claim:

A cartridge case comprising a base and circularly shaped side walls integrally formed from elastic thermoplastic material, said side walls being in the form of a hollow cylinder having a constant external diameter along its length above said base, a charge contained in said case above said base, a detonating cap in said base, a sharpedged and imperforate metallic disc having a circular peripheral edge spaced above said charge and having said peripheral edge embedded in the inner surface of said side Walls, said disc having an outer diameter greater than the inner diameter of said side walls but less than the outer diameter of said side walls, and means forming a spacer between said disc and the upper end of said charge.

References Cited in the file of this patent UNITED STATES PATENTS Clark Dec. 26, Maas Oct. 14, Shazor June 23, Rurnsey Feb. 9,

FOREIGN PATENTS Great Britain Apr. 18, France Oct. 3, Great Britain May 14, 

